The present invention relates to a porous surface or structure and a method for forming the same, which uses a directed energy beam to selectively remelt a powder to produce a part. The energy beam may include a laser beam, and an electron beam or the like. In particular, this invention relates to a computer-aided laser apparatus, which sequentially remelts a plurality of powder layers to form unit cells to build the designed part in a layer-by-layer fashion. The present application is particularly directed toward a method of forming a porous and partially porous metallic structure.
The field of free-form fabrication has seen many important recent advances in the fabrication of articles directly from computer controlled databases. These advances, many of which are in the field of rapid prototyping of articles such as prototype parts and mold dies, have greatly reduced the time and expense required to fabricate articles, particularly in contrast to conventional machining processes in which a block of material, such as a metal, is machined according to engineering drawings.
One example of a modern rapid prototyping technology is the selective laser sintering process practiced by systems available from 3D Systems Valencia Calif. According to this technology, articles are produced in layer-wise fashion from a laser-fusible powder that is dispensed one layer at a time. The powder is fused, remelted or sintered, by the application of laser energy that is directed in raster-scan fashion to portions of the powder layer corresponding to a cross section of the article. After the fusing of the powder on one particular layer, an additional layer of powder is dispensed, and the process repeated, with fusion taking place between the current layer and the previously laid layers until the article is complete. Detailed descriptions of the selective laser sintering technology may be found in U.S. Pat. No. 4,863,538, U.S. Pat. No. 5,017,753, U.S. Pat. No. 5,076,869 and U.S. Pat. No. 4,944,817. The selective laser remelting and sintering technologies have enabled the direct manufacture of solid or dense three-dimensional articles of high resolution and dimensional accuracy from a variety of materials including wax, metal powders with binders, polycarbonate, nylon, other plastics and composite materials, such as polymer-coated metals and ceramics.
The field of the rapid prototyping of parts has, in recent years, made large improvements in broadening high strain, high density, parts for use in the design and pilot production of many useful articles, including metal parts. These advances have permitted the selective laser remelting and sintering processes to now also be used in fabricating prototype tooling for injection molding, with expected tool life in access of ten thousand mold cycles. The technologies have also been applied to the direct fabrication of articles, such as molds, from metal powders without a binder. Examples of metal powder reportedly used in such direct fabrication include two-phase metal powders of the copper-tins, copper-solder (the solder being 70% lead and 30% tin), and bronze-nickel systems. The metal articles formed in these ways have been quite dense, for example, having densities of up to 70% to 80% of fully dense (prior to any infiltration). Prior applications of this technology have strived to increase the density of the metal structures formed by the melting or sintering processes. The field of rapid prototyping of parts has focused on providing high strength, high density, parts for use and design in production of many useful articles, including metal parts.
However, while the field of rapid prototyping has focused on increasing density of such three-dimensional structures, the field has not focused its attention on reducing the density of three-dimensional structures. Consequently, applications where porous and partially porous metallic structures, and more particularly metal porous structures with interconnected porosity, are advantageous for use have been largely ignored. One such reference which hasn't ignored metal porous structures with interconnected porosity and having a relatively low density is commonly assigned U.S. patent application Ser. No. 10/704,270 filed on Nov. 7, 2003, the disclosure of which is hereby incorporated herein by reference. Although this reference has provided various techniques in creating laser produced porous surfaces, still greater technologies are needed in this area.
In either case, the present invention is equally adapted for building porous structure having a high density or a low density.